Antireflection coating and assembly having synthesized layer of index of refraction



March 11, 1969 F. c. ROCK 3,432,225

ANTIREFLECTION comma AND ASSEMBLY HAVING SYNTHESIZED LAYER OF INDEX OFREFRACTION Filed May 4, 1964 WIIIIIIIIIII 7 & 12 i flafi'xmazza 'zeaa'mM F I 2 u w I m F I 9. 3 a) aveeng 1%; (4) 90.

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Frank C. Rock I2 BY 67 44 @Z ZQ Attorneys United States Patent 3,432,225ANTIREFLECTION COATING AND ASSEMBLY HAVING SYNTHESIZED LAYER OF INDEX OFREFRACTION Frank C. Rock, Santa Rosa,

Coating Laboratory, Inc., poration of California Filed May 4, 1964, Ser.No. 364,479 US. Cl. 350-164 Claims Int. Cl. G02b 1/10; B29d 11/00Calif., assignor to Optical Santa Rosa, Calif., a cor- ABSTRACT OF THEDISCLOSURE This invention relates to an antirefiection coating, assemblyand method and more particularly to an antirefiection coating, assemblyand method in which four layers and two or more materials are utilizedin the coating.

One and two layer antirefiection coatings are Well known to thoseskilled in the art and are of generally low efliciency. A three-layerantirefiection coating is disclosed in copending application Ser. No.136,479, filed Sept. 7, 1961, now United States Letters Patent No.3,185,020, which requires the use of three different materials: a firstlayer of a material having a medium index of refraction; a second layerof a material having a high index of refraction; and a third layer of amaterial having a low index of refraction. Such a coating requires thateach of i the three layers be controlled in thickness and be controlledin refractive index. As the refractive index of the substrate on whichthe coating is mounted is changed, the refractive index of the firstlayer has to be changed accordingly. There is a direct relationshipbetween the refractive index required for the first layer and thesubstrate in order to be able to obtain a successful high efiiciencyantirefiection coating of the three layer tape. Because of thisrelationship between the refractive index of the substrate and therefractive index of the first layer, it has been diflicult in suchthree-layer coatings to control the shape of the antirefiection curve,particularly at the center of the spectrum for which the coating is tobe effective, e.g., from 500 to 550 millimicrons, because thereflectance in this region is primarily dependant upon the refractiveindex of the first layer of the three layer antirefiection coating.Thus, if the first layer has an index of refraction which is too low,the center of the antireflection curve can rise to well over one-half of1% so that the primary advantage over a single layer of magnesiumfluoride coating is lost. In order to make a three-layer coating on atype of substrate which is commonly used, e.g., a substrate having arefractive index of 1.52, it is desirable that this first layer of thecoating have an index of refraction of 1.65. At the present time, thereis no reproducible material which has this refractive index which can beutilized for the first layer. For this reason, there is a necessity tofind an alternative method for creating the effect of such a materialout of the materials which at present are known to exist to 3,432,225Patented Mar. 11, 1969 provide a high efiiciency antirefiection coatingand assembly which is capable of being manufactured under productionconditions.

In general, it is an object of the present invention to provide a highefficiency antirefiection coating and an assembly for the manufacture ofthe same which overcomes the above named disadvantages.

Another object of the invention is to provide an antireflection coatingand assembly of the above character in which a single layer of desiredrefractive index is synthesized by the use of two or more thin layers ofmaterials having higher and lower refractive indices.

Another object of the invention is to provide an antirefiection coatingand assembly in which the outer or final layer is chosen for maximumdurability and for a refractive index as low as possible and in whichthe next to the outer or final layer is chosen to provide maximumbandwidth.

Another object of the invention is to provide an antireflection coatingand assembly which can be utilized with substrates having differentindices of refraction.

Another object of the invention is to provide an antireflection coatingand assembly of the above character in which an additional layer can bereadily incorporated in the coating and assembly to withstandundesirable environments without substantially affecting the spectralcharacteristics of the coating and assembly.

Another object of the invention is to provide an antireflection coatingand assembly of the above character which utilizes four layers and atleast two materials in the coating.

Another object of the invention is to provide an antireflection coatingand assembly which does not have undesirable colorimetric properties.

Another object of the invention is to provide an antireflection coatingand assembly of the above character which is particularly adapted foruse with a synthetic plastic material as a substrate.

Another object of the invention is to provide an antirefiection coatingand assembly of the above character which can be readily andeconomically manufactured under production conditions.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments are set forthin' detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE 1 is a cross sectional view on a greatly enlarged scale of anantirefiection coating and assembly incorporating my invention.

FIGURE 2 is a polar coordinate phase diagram showing the relationshipbetween reflectance amplitude and phase between the reflected ray andthe incident ray at one particular wavelength at the center of the bandwhich is antireflected by the coating and assembly shown in FIGURE 1.

FIGURE 3 is a curve showing the reflectance of a typical antirefiectioncoating incorporating my invention.

FIGURE 4 is a cross sectional view of an assembly on a greatly enlargedscale of an antirefiection coating and assembly also incorporating myinvention using substrates having higher indices of refraction.

FIGURES is a polar coordinate phase diagram showing the relationshipbetween reflectance amplitude and phase between the reflected ray andthe incident ray for one particular wavelength in the center of the bandwhich is antireflected by the coating and assembly shown in FIGURE 4.

In general, my optical assembly consists of a substrate with anantirefiection coating disposed on a surface of the substrate. Theantirefiection coating is nonabsorbing and substantially colorless andconsists of first and second layers counting from the substrate. Thefirst and second layers are each formed of a material having a differentindex of refraction and each having an optical thickness of less thanone quarater of the design wavelength of the antirefiection coating andsynthesizing the effect of a layer having an index of refraction betweenthe indices of refraction of the two materials and an optical thicknessof approximately one quarter of the design wavelength of theantirefiection coating. At least one additional layer is disposed on thefirst and second layers to complete the antirefiection coating.

More particularly, as shown in FIGURE 1 of the drawings my opticalassembly consists of a transparent substrate 11, having a normal lightreflecting surface of a suitable material, such as glass, which has anindex of refraction (N) that can vary from 1.45 to as high as 5.2. Anantirefiection coating 12 is deposited upon the one surface of thesubstrate 11 and consists of four transparent, substantially colorlesslayers 16-19 inclusive which are formed of at least two differentmaterials, in which one of the materials has a high index of refractionand the other has a low index of refraction.

In order to achieve maximum bandwidth for the antireflection coating, itis desirable that the material with a low index of refraction have aslow an index of refraction as possible. One material found to beparticularly satisfactory for use as the low index material is magnesiumfluoride (MgF which has an index of refraction of 1.38. Another materialwhich can serve as a satisfactory low index material is silicon dioxide(SiO .which has an index of refraction of 1.45 with only some sacrificein bandwidth of the antirefiection coating. In general the low indexmaterial, in addition to having a low index of refraction, should berelatively hard and durable. Magnesium fluoride is generally quitesatisfactory because it is relatively durable and provides a relativelywide bandwidth for the antirefiection coating.

For the material having a high index of refraction, there is a range ofvalues for the high index of refraction which will give the bestbandwidth for the antirefiection coating and at the same time make itpossible to achieve low reflection values for the antirefiectioncoating. This range for the high index material is from 2.00 to 2.10. Ifthe refractive index is substantially higher than 2.10, the bandwidth ofthe antirefiection coating narrows substantially In general, with anindex of refraction of over 2.10, it is still possible to obtainexcellent reduction of reflection throughout the central region, but thesides of the antirefiection curve move in so that the bandwidth issubstantially narrower. When the refractive index of the high indexmaterial becomes lower than 2.00, the bandwidth is increased, but thecentral portion of the refiectance curve raises to thereby decrease theefficiency of the antirefiection coating. One material found to besuitable for use as material having a high index of refraction iszirconium oxide which has an index of refraction of approximately 2.08.Other material which can be utilized are those of the type disclosed inPatent No. 3,034,924.

The first and second layers 16 and 17 of the antirefiection coating 12counting from the substrate 11 can be called thin layers and are used tosynthesize a layer having an optical thickness of one-quarter of thedesign wavelength for the antirefiection coating and of an intermediaterefractive index between that of the substrate 11 and the layer 18. Bythe method herein described, this quarter wave layer of intermediaterefractive index is synthesized by utilizing thin layers of materialsthat have lower and higher indices of refraction than the indexofrefraction desired. This is accomplished by depositing a first layer 16of high index material to an optical thickness substantally less thanone quarter of the design wavelength for the antirefiection coatingfollowed by 3 second layer of the material having a low indexofrefraction to a thickness also substantially less than one quarter ofthe design wavelength. The effect achieved by these two thin layers forreasons hereinafter described is a layer of intermediate refractiveindex and having an optical thickness of one-quarter of the designwavelength for the antirefiection coating which makes it possible tocreate an optimum antirefiection coating for substrate refractiveindices varying from 1.45 to greater than 1.76.

At least one additional layer is deposited on the first and secondlayers. There a final or outer layer 19 is formed of the material havinga low index of refraction and is deposited to a depth of one-quarter thedesign wavelength to provide a layer which has maximum durability andwhich properly antirefiects the substrate. Still another layer, which isthe next to the outer layer, is layer 18 which is provided to increasethe bandwidth of the antirefiection coating.

Layer 18 is a relatively thick layer and is deposited as homogenously aspossible after the layers 16 and 17 have been deposited. It is formed ofthe material having the high index of refraction and is deposited to anoptical depth equal to one-half of the design wavelength of theantirefiection coating.

In FIGURE 2, there is shown a phase diagram indicating the method bywhich the antirefiection coating and assembly shown in FIGURE 1 isdesigned and how it functions. First, there is shown in FIGURE 2, threecurves identified as 1a, 1b and 10, which start from the axis at indicesof refraction indicated as 1.45, 1.52 and 1.65, respectively. Theseindices of refraction indicate representative indices for the substrate11. As can be seen from the phase diagram, as the index of refraction ofthe substrate increases, the reflectance amplitude is higher. Curves 1a,1b and 1c indicate the phase relationship between the incident ray andthe reflected ray at one particular wavelength and show what occurs whenthe first thin layer 16 is deposited on the substrates having thedifferent indices of refraction. Thus, it can be seen that as the indexof refraction of the substrate increases, the curve measured in degreesof arc length indicates the relative thickness of the first layer.Hence, as the refractive index of the substrate increases, layer 16initially increases slightly in thickness and thereafter becomes thinnerand thinner to arrive at the point where the curve identified as No. 2,which represents the second layer 17, commences.

As can be seen, curves for the second layer commence at the terminationof the curves 1 and terminate at the 180 axis. As the refractive indexof the substrate increases, the second layer 17 must become thinner.Termination at the 180 axis is desirable in order to make thereflectance curve for the antirefiection coating symmetrical. Ifsymmetry is not desired, it is not absolutely essential that a return bemade to the 180 axis. In certain cases, it may be desirable to goslightly beyond the 180 axis. From the phase diagram it can be seen thatthe first and second layers are both deposited in optical thicknesseswhich are substantially less than one-quarter of the design wavelengthof the antirefiection coating to synthesize a layer having an index ofrefraction between the high and low indices of the materials used and anoptical thickness of one-quarter of the design wavelength of theantirefiection coating.

The third layer 18 is a high index layer and starts from the terminationof the curve No. 2 at or near the 180 axis and goes throughapproximately 360 as shown in the phase diagram to return to the 180axis to show that the third layer is deposited to an optical depthsubstantially equal to one-half of the design wavelength of theantirefiection coating. Thus, the curve 3 goes through a complete circleor 360. It is important that the third layer terminate at the 180 axisso that the fourth layer can start at the 180 axis. This is because thefourth layer has an optical thickness of one-quarter of the designwavelength of the antirefiection coating and it is desirable to end upat zero or close to zero reflectance with the fourth layer. Thus, as canbe seen, curve 4 for the fourth layer 19 is a semicircle and begins onthe 180 axis and terminates at or near zero.

From the foregoing method using phase diagram design technique it can beseen that the optical thickness to which the first and second layersmust be deposited in order to synthesize a layer having an intermediateindex of refraction and an optical thickness of one-quarter of thedesign wavelength of the antireflection coating can be readilydetermined.

By way of example, two optical assemblies with antireflection coatingsincorporating my invention are set forth below with the opticalthickness designated by the wavelength in millimicrons at which thelayer is a quarter wave thick. (Note.-An alternative would be to divideall values in the table by 515).

The reflectance curve for an antireflection coating constructed inaccordance with the second example in which the design wavelength is 515millimicrons is shown in FIGURE 3. From this curve, it can be seen thatthe antireflection coating has a relatively wide band width and has avery low reflectance, i.e., below 0.2% visual reflectance.

In FIGURE 4, there is shown an optical assembly incorporating the samedesign principles as hereinbefore described but for a substrate whichhas a substantially higher index of refraction as, for example, fromv1.95 to 6.0 and which includes a material such as germanium which has anindex of refraction of 4.0. The antireflection coating 12 is made up ofthe four layers 16, 17, 18 and 19 formed of two materials havin high andlow indices of refraction. One suitable material having a low index ofrefraction is silicon monoxide which has an index of refraction of 1.85.One suitable material having a high index of refraction is germaniumhaving an index of refraction of 4.0 as hereinbefore pointed out. Aswith the embodiment hereinbefore described, the first two layers 16 and17 are deposited for the purpose of lowering the effective refractiveindex of the substrate to a value such that it can be perfectlyantirefiected by the fourth layer having a thickness of one-quarter ofthe design wavelength of the antireflection coating. In the embodimenthereinbefore described, the substrate had an index of refraction inwhich it was desired to increase or raise the effective refractive nidexof the substrate to a value so that it could be properly antireflectedby the fourth layer.

In the embodiment shown in FIGURE 4 the first layer 16 is formed of amaterial having a low index of refraction. This layer is represented bythe curve 1 in the phase diagram shown in FIGURE 5. As can be noted fromFIGURES 2 and 5, the centers of the arcs, semicircles and circles moveoutward as a refractive index increases. Then also the arcs, semicirclesnad circles are formed by rotation in a clockwise direction. Thus, forthe low index layer 16, the curve 1 moves upwardly and clockwise toindicate a layer which is deposited to an optional thicknesssubstantially less than one-quarter of the design wavelength for theantireflection coating. Similarly, the second layer 17 is a thin layerof the high index material and is represented by curve 2 in FIGURE 5. Italso is deposited to a depth substantially less than one-quarter of thedesign wavelength of the antireflection coating. The first and secondlayers in effect provide a synthesized layer which has an intermediateindex of refraction and which has a thickness of one-quarter of thedesign wavelength. The third layer 18 is next deposited and is-formed ofa material which has a high index of refraction and is deposited to anoptical depth equal to one-half of the design wavelength of theantireflection coating. Thus, as shown in FIGURE 5 by the #3 curve, thecurve starts at axis, travels through 360 and ends at the 180 axis. Thesecond and third layers may be formed of the same material since theyshould both be of a high index of refraction. The fourth or outer layer19 is next deposited and is formed of a material having a low index ofrefraction and is deposited to a depth of one-quarter of the designwavelength of the antireflection coating. This is shown by curve 4 inFIGURE 5. The curve starts at 180 axis and terminates at or near thezero intersection.

The crossover point to determine whether the materials of the type shownin FIGURE 1 should be utilized or the ones shown in FIGURE 4 should beutilized is determined by the refractive index of the final or fourthlayer. A substrate is perfectly antireflected by the final layer whenthe substrate has an index of refraction which is equal to the index ofrefraction of the final layer squared. In other words, if the finallayer has a refractive index of 1.5, the crossover point is that of asubtrate having a refractive index of 2.25. Where magnesium fluoride(n=1.38) is used for the outer layer, the crossover point is (1.38)which is approximately equal to 1.90. With a substrate with this index,magnesium fluoride is almost a perfect coating all by itself. Withindices of refraction such as that shown in FIGURE 4, magnesium fluorideis not a suitable material. A more desirable low index material issilicon monoxide which has an index of refraction of 1.85. This is anideal antireflection coating for a substrate having a refractive indexof (1.85) which is equal to approximately 3.4.

By way of example the substrates having the following indices ofrefraction can be utilized with the following outer or fourth layers.

Outer Layer Mg e SiO ZnS

By the foregoing method, it can be seen that layers are deposited on thesubstrate to modify the effective refractive index of the substrate to anew value that is properly antirefiected by the material utilized forthe outer layer. The reflectance can be brought down to zero but thiswould have the undesired effect of narrowing the bandwidth. Also, if thereflectance is brought down to zero, there is no green light andundesirable colormetric properties are exhibited by the coating. Forexample, it may appear to be blue or red and not a pleasing grey whichis one of the desired colors for the antireflection coating. Thesedesirable colormetric properties can be achieved by not returning thefourth layer exactly to zero. In the foregoing embodiments, it is thefinal layer which does all of the antireflecting. The third layer isutilized solely for increasing the band width of the antireflectioncoating.

I have found that the antireflection coating herein described can alsobe deposited upon synthetic plastic substrates without any difficulty.In general, synthetic plastics have an index of refraction ranging from1.45 to 1.62. By utilizing the four layer method hereinbefore described,it is possible to adjust for the index of refraction of the syntheticplastic substrate merely by adjusting the thickness of the first andsecond layers deposited upon the synthetic plastic. Because syntheticplastics cannot withstand too much heat, it is necessary at times toutilize materials which can be deposited on a cold surface Whendepositing on a cold surface, it may be necessary to utilize differentmaterials because the materials when deposited on a cold surface mayhave a different index of refraction. For example, titanium dioxide,when deposited on a hot surface, has a refractive index of approximately2.3, but when deposited on a cold surface, drops to 2.0 to 2.1 and thusforms a material suitable for an effective antirefiection coating forsynthetic plastics utilizing the method herein disclosed.

Although the coatings hereinbefore described have been described asutilizing only two materials, if desired, more than two materials can beused. Also, although only four layers have been described in theembodiments herein disclosed, an additional fifth layer can be providedto protect the filters from undesirable environments. Thus, the last orfourth layer can be deposited by evaporation so that approximatelythree-fourths of the layer has been deposited. The fourth layer then canbe completed by utilizing a fifth layer of a material of a differenttype as, for example, one of a higher refractive index (e.g., A1 0 andSiO which is more durable to unfavorable environments. Thus, it ispossible to achieve an antireflection coating which has substantiallythe same spectral characteristics but which is protected fromunfavorable environments by the fifth layer. In fact, the fifth layer isnot a separate layer but is actually substituted for a part of thefourth layer.

It is apparent from the foregoing that I have provided an improvedantirefiection coating and assembly and method for formation of thesame. The antirefiection coating is particularly advantageous in that itis possible to form the coating from only two materials while stillobtaining a very high efiiciency. The method, in particular, makes itpossible to synthesize a certain layer so that it will effectivelyrepresent a layer of a different index of refraction and a differentoptical thickness.

In particular, my method has made it possible to apply antireflectioncoatings to substrates having higher indices of refraction as, forexample, in the coating of optical systems which employ high indexglasses and certain plastics as substrates.

I claim:

1. In an article of the character described, a substrate having a normallight reflecting surface and an anti-reflection coating disposed on thesurface, the antirefiection coating comprising at least four layersidentified as the first, second, third and fourth layers counting fromthe substrate, the first and second layers being formed of materialshaving different indices of refraction and having optical thicknessessubstantially less than one-quarter of the design wavelength of theantireflection coating and in effect synthesizing a layer having andndexof refraction intermediate the indices of refraction of the materialforming the first and second layers and serving to modify the effectiverefractive index of the substrate, said first and second layers having acombined optical thickness equal to approximately one-quarter of thedesign wavelength of the antirefiection coating, said third layer beingformed of a material having a high index of refraction and said fourthlayer being formed of material having a low index of refraction, saidthird layer having an optical thickness substantially greater than theoptical thickness of said fourth layer.

2. An article as in claim 1 wherein said coating is formed of only twomaterials and wherein one of said materials has a high index ofrefraction and the other said material has a low index of refraction.

3. In an optical assembly, a substrate having a normal light reflectingsurface, an antirefiection coating disposed on the surface, theantirefiection coating comprising first, second, third and fourth layerscounting from the substrate, the first and second layers being formed ofmaterials having different indices of refraction, and having opticalthicknesses substantially less than one-quarter of the design wavelengthof the antireflection coating and in effect synthesizing a layer havingan index of refraction intermediate the indices of refraction of thematerials forming the first and second layers and serving to modify theeffective refractive index of the substrate, sa'id first and secondlayers having a combined optical thickness equal to approximatelyone-quarter of the design wavelength of the antireflection coating, saidthird layer being formed of a material having a high index of refractionand having an optical thickness of substantially one-half of the designwavelength of the antirefiection coating, said fourth layer being formedof a material having a low index of refraction and having an opticalthickness of substantially one-quarter of the design wavelength of theantireflection coating.

4. An assembly as in claim 3 wherein said first, second, third andfourth layers are formed of at least two materials, one of said twomaterials having a high index of refraction and the other of said twomaterials having a low index of refraction.

5. An optical assembly as in claim 3 wherein the first layer is formedof a material having a high index of refraction and wherein the secondlayer is formed of a material having a low index of refraction.

6. An optical assembly as in claim 3 wherein the first layer is formedof a material having a low index of refraction and wherein the secondlayer is formed of a material having a high index of refraction.

7. An optical assembly as in claim 3 wherein said substrate is formed ofa synthetic plastic.

8. An optical assembly as in claim 3 wherein the outer layer is formedof magnesium fluoride.

9. An optical assembly as in claim 3 wherein the outer layer is formedof silicon dioxide.

10. An optical assembly as in claim 3 wherein the outer layer is formedof zinc sulfide.

11. An optical assembly as in claim 3 wherein the outer layer is formedof cadmium selenide.

12. In an optical assembly, a substrate having a refiecting surface andan antirefiection coating disposed on the surface, the antireflectioncoating being comprised of first, second, third and fourth layerscounting from the substrate, the first and second layers each beingformed of a material having a different index of refraction and havingoptical thicknesses substantially less than one-quarter of the designwavelength of the antireflection coating and serving to modify theeffective refractive index of the substrate, said first and secondlayers having a combined optical thickness of substantially one quarterof the design wavelength, the third layer having an optical thickness ofsubstantially one-half of the design wavelength of the antirefiectioncoating and the fourth layer having an optical thickness ofsubstantially one-fourth of the design wavelength of the antirefiectioncoating, said first, second, third and fourth layers being formed of twomaterials, one of the materials having a high index of refraction andthe other of the materials having a low index of refraction, the firstand second layers being formed of materials having high and low indicesof refraction, the third layer being formed of a material having a highindex of refraction and the fourth layer being formed of a materialhaving a low index of refraction.

13. An assembly as in claim 12 wherein the first layer is formed of amaterial having a low index of refraction and the second layer is formedof a material having a high index of refraction.

14. An assembly as in claim 12 wherein the first layer is formed of amaterial having a high index of refraction and the second layer isformed of a material having a low index of refraction.

15. In an antirefiection coating for use on a substrate having areflecting surface, the antireflection coating comprising first, second,third and fourth layers, the first layer being adapted to be disposed onthe surface of the substrate, the first and second layers being formedof materials having ditferent indices of refraction and having anoptical thickness substantially less than one-quarter of the designwavelength of the antirefiection coating said first and second layershaving a combined optical thickness of one-quarter of the designwavelength and being adapted to modify the effective refractive index ofthe substrate, the third layer having an optical thickness of one-halfof the design wavelength of the antirefiection coating and a fourthlayer having an optical thickness of one-fourth of the design wavelengthof the antirefiection coating, said first, second, third and fourthlayers being formed of two different materials, one of the materialshaving a high index of refraction and the other of the materials havinga low index of refraction, the first and second layers being formed oflayers of the two materials, the third layer being formed of materialhaving a high index of refraction and the fourth layer being formed of amaterial having a low index of refraction.

References Cited UNITED STATES PATENTS 10 3,147,132 9/1964 Geffcken.3,185,020 5/1965 Thelen 350164 3,235,397 2/1966 Millendorfer 350l64OTHER REFERENCES Kruse, McGlauchin and McQuistan; Elements of InfraredTechnology, Generation, Transmission, and Detection; 1962; Published byJohn Wiley 8: Sons.

Osterberg and Kashdan: Abstract 53 and Pride and Kashdan, Abstract 54;42 I. O. 5A.291, April, 1952.

Turner, A. F.: Some Current Developments in Multilayer Optical Films;Reprinted from Le Journal de Phisique et le Radivin; vol. 11, pp.444457; July, 1950.

U.S. Defense Supply Agency: Military-Handbookl4l; Optical Design; Oct.5, 1962, pp. 21-66 and 21-67.

DAVID SCHONBERG, Primary Examiner.

T. H. KUSMER, Assistant Examiner.

U.S. Cl. X.R. 11733.3

